Detonation or combustion knock in an internal combustion engine is the spontaneous combustion of a major portion of the air-fuel charge in the cylinder. Detonation results in an extremely rapid local pressure rise and produces a sharp metallic sounding knock. Detonation is caused by three things, namely; the auto ignition temperature of the air-fuel mixture, the ignition lag and the flame speed propagation within the mixture. The detonation phenomenon is usually investigated in the laboratory. One method of inhibiting detonation is by the use of an enriched fuel mixture. Using a 10 percent enriched fuel-to-air mixture provides an improved margin of safety while at the same time does not seriously degrade the fuel economy of the engine. The shape of the combustion chamber and the placement of the valves and the spark plug also effects the detonation characteristics of the engine.
Aside from the mechanical design and the fuel-to-air mixture there is significant influence on the detonation characteristics of an engine due to the environmental conditions in which it operates. This includes both the air temperature and the barometric pressure. With the increasing use of turbocharger equipped general aviation aircraft flying at altitudes up to 30,000 ft., it has become necessary to investigate the detonation characteristics of aircraft engines under environmental conditions which are not practical to duplicate in the laboratory. Available laboratory instruments are not considered suitable for applications in flying aircraft. This is primarily due to the relatively large size, heavy weight and high power consumption of existing laboratory instruments. In addition, laboratory instruments are not designed to function at 20,000 ft. altitudes wherein only 5 percent or less of the sea level air pressure remains.
Two systems for investigating the detonation characteristics of an engine are known. The first system was developed about 35 years ago specifically for commercial aircraft. The system consisted of several subassemblies which were permanently installed in the aircraft and the results monitored by the flight engineer. With the advent of jet powered commercial aircraft this system became obsolete and has been out of production for many years. The second system, also no longer in production, was developed for the conduct of both laboratory and flight investigations of the detonation phenomenon. This system had a very definite arcing problem when called upon to operate at altitudes above 20,000 ft. This second system also required considerable space and electrical power drain from the aircraft.
My invention overcomes the shortcomings of the two earlier systems. As reduced to practice my invention comprises an analyzer and a display unit which in combination weigh approximately 10 lbs. and occupy approximately one-third of a cubic ft. of volume.